What is the 15th letter of the Greek alphabet?

The 15th letter of the Greek alphabet is Omicron (Ο, Ο). It is the middle letter of the second row in the classical order of the Greek alphabet. Omicron is derived from the Phoenician letter Ayin and represents the sound /o/ as in "lot" or "dog" in English. It is pronounced as "ahy" in Modern Greek. Omicron is used in various fields, including mathematics, physics, engineering, and it holds significant importance in Greek language and culture.